/* ----------------------------------------------------------------------
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.
*
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*
* Project: 	    CMSIS DSP Library
* Title:        arm_fir_q7.c
*
* Description:  Q7 FIR filter processing function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup FIR
 * @{
 */

/**
 * @param[in]   *S points to an instance of the Q7 FIR filter structure.
 * @param[in]   *pSrc points to the block of input data.
 * @param[out]  *pDst points to the block of output data.
 * @param[in]   blockSize number of samples to process per call.
 * @return 	none.
 *
 * <b>Scaling and Overflow Behavior:</b>
 * \par
 * The function is implemented using a 32-bit internal accumulator.
 * Both coefficients and state variables are represented in 1.7 format and multiplications yield a 2.14 result.
 * The 2.14 intermediate results are accumulated in a 32-bit accumulator in 18.14 format.
 * There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.
 * The accumulator is converted to 18.7 format by discarding the low 7 bits.
 * Finally, the result is truncated to 1.7 format.
 */

void arm_fir_q7(
    const arm_fir_instance_q7 *S,
    q7_t *pSrc,
    q7_t *pDst,
    uint32_t blockSize)
{

#ifndef ARM_MATH_CM0_FAMILY

    /* Run the below code for Cortex-M4 and Cortex-M3 */

    q7_t *pState = S->pState;                      /* State pointer */
    q7_t *pCoeffs = S->pCoeffs;                    /* Coefficient pointer */
    q7_t *pStateCurnt;                             /* Points to the current sample of the state */
    q7_t x0, x1, x2, x3;                           /* Temporary variables to hold state */
    q7_t c0;                                       /* Temporary variable to hold coefficient value */
    q7_t *px;                                      /* Temporary pointer for state */
    q7_t *pb;                                      /* Temporary pointer for coefficient buffer */
    q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */
    uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
    uint32_t i, tapCnt, blkCnt;                    /* Loop counters */

    /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    /* pStateCurnt points to the location where the new input data should be written */
    pStateCurnt = &(S->pState[(numTaps - 1u)]);

    /* Apply loop unrolling and compute 4 output values simultaneously.
     * The variables acc0 ... acc3 hold output values that are being computed:
     *
     *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]
     *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]
     *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]
     *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]
     */
    blkCnt = blockSize >> 2;

    /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
     ** a second loop below computes the remaining 1 to 3 samples. */
    while(blkCnt > 0u)
    {
        /* Copy four new input samples into the state buffer */
        *pStateCurnt++ = *pSrc++;
        *pStateCurnt++ = *pSrc++;
        *pStateCurnt++ = *pSrc++;
        *pStateCurnt++ = *pSrc++;

        /* Set all accumulators to zero */
        acc0 = 0;
        acc1 = 0;
        acc2 = 0;
        acc3 = 0;

        /* Initialize state pointer */
        px = pState;

        /* Initialize coefficient pointer */
        pb = pCoeffs;

        /* Read the first three samples from the state buffer:
         *  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
        x0 = *(px++);
        x1 = *(px++);
        x2 = *(px++);

        /* Loop unrolling.  Process 4 taps at a time. */
        tapCnt = numTaps >> 2;
        i = tapCnt;

        while(i > 0u)
        {
            /* Read the b[numTaps] coefficient */
            c0 = *pb;

            /* Read x[n-numTaps-3] sample */
            x3 = *px;

            /* acc0 +=  b[numTaps] * x[n-numTaps] */
            acc0 += ((q15_t) x0 * c0);

            /* acc1 +=  b[numTaps] * x[n-numTaps-1] */
            acc1 += ((q15_t) x1 * c0);

            /* acc2 +=  b[numTaps] * x[n-numTaps-2] */
            acc2 += ((q15_t) x2 * c0);

            /* acc3 +=  b[numTaps] * x[n-numTaps-3] */
            acc3 += ((q15_t) x3 * c0);

            /* Read the b[numTaps-1] coefficient */
            c0 = *(pb + 1u);

            /* Read x[n-numTaps-4] sample */
            x0 = *(px + 1u);

            /* Perform the multiply-accumulates */
            acc0 += ((q15_t) x1 * c0);
            acc1 += ((q15_t) x2 * c0);
            acc2 += ((q15_t) x3 * c0);
            acc3 += ((q15_t) x0 * c0);

            /* Read the b[numTaps-2] coefficient */
            c0 = *(pb + 2u);

            /* Read x[n-numTaps-5] sample */
            x1 = *(px + 2u);

            /* Perform the multiply-accumulates */
            acc0 += ((q15_t) x2 * c0);
            acc1 += ((q15_t) x3 * c0);
            acc2 += ((q15_t) x0 * c0);
            acc3 += ((q15_t) x1 * c0);

            /* Read the b[numTaps-3] coefficients */
            c0 = *(pb + 3u);

            /* Read x[n-numTaps-6] sample */
            x2 = *(px + 3u);

            /* Perform the multiply-accumulates */
            acc0 += ((q15_t) x3 * c0);
            acc1 += ((q15_t) x0 * c0);
            acc2 += ((q15_t) x1 * c0);
            acc3 += ((q15_t) x2 * c0);

            /* update coefficient pointer */
            pb += 4u;
            px += 4u;

            /* Decrement the loop counter */
            i--;
        }

        /* If the filter length is not a multiple of 4, compute the remaining filter taps */

        i = numTaps - (tapCnt * 4u);
        while(i > 0u)
        {
            /* Read coefficients */
            c0 = *(pb++);

            /* Fetch 1 state variable */
            x3 = *(px++);

            /* Perform the multiply-accumulates */
            acc0 += ((q15_t) x0 * c0);
            acc1 += ((q15_t) x1 * c0);
            acc2 += ((q15_t) x2 * c0);
            acc3 += ((q15_t) x3 * c0);

            /* Reuse the present sample states for next sample */
            x0 = x1;
            x1 = x2;
            x2 = x3;

            /* Decrement the loop counter */
            i--;
        }

        /* Advance the state pointer by 4 to process the next group of 4 samples */
        pState = pState + 4;

        /* The results in the 4 accumulators are in 2.62 format.  Convert to 1.31
         ** Then store the 4 outputs in the destination buffer. */
        acc0 = __SSAT((acc0 >> 7u), 8);
        *pDst++ = acc0;
        acc1 = __SSAT((acc1 >> 7u), 8);
        *pDst++ = acc1;
        acc2 = __SSAT((acc2 >> 7u), 8);
        *pDst++ = acc2;
        acc3 = __SSAT((acc3 >> 7u), 8);
        *pDst++ = acc3;

        /* Decrement the samples loop counter */
        blkCnt--;
    }


    /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
     ** No loop unrolling is used. */
    blkCnt = blockSize % 4u;

    while(blkCnt > 0u)
    {
        /* Copy one sample at a time into state buffer */
        *pStateCurnt++ = *pSrc++;

        /* Set the accumulator to zero */
        acc0 = 0;

        /* Initialize state pointer */
        px = pState;

        /* Initialize Coefficient pointer */
        pb = (pCoeffs);

        i = numTaps;

        /* Perform the multiply-accumulates */
        do
        {
            acc0 += (q15_t) * (px++) * (*(pb++));
            i--;
        }
        while(i > 0u);

        /* The result is in 2.14 format.  Convert to 1.7
         ** Then store the output in the destination buffer. */
        *pDst++ = __SSAT((acc0 >> 7u), 8);

        /* Advance state pointer by 1 for the next sample */
        pState = pState + 1;

        /* Decrement the samples loop counter */
        blkCnt--;
    }

    /* Processing is complete.
     ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
     ** This prepares the state buffer for the next function call. */

    /* Points to the start of the state buffer */
    pStateCurnt = S->pState;

    tapCnt = (numTaps - 1u) >> 2u;

    /* copy data */
    while(tapCnt > 0u)
    {
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;
        *pStateCurnt++ = *pState++;

        /* Decrement the loop counter */
        tapCnt--;
    }

    /* Calculate remaining number of copies */
    tapCnt = (numTaps - 1u) % 0x4u;

    /* Copy the remaining q31_t data */
    while(tapCnt > 0u)
    {
        *pStateCurnt++ = *pState++;

        /* Decrement the loop counter */
        tapCnt--;
    }

#else

    /* Run the below code for Cortex-M0 */

    uint32_t numTaps = S->numTaps;                 /* Number of taps in the filter */
    uint32_t i, blkCnt;                            /* Loop counters */
    q7_t *pState = S->pState;                      /* State pointer */
    q7_t *pCoeffs = S->pCoeffs;                    /* Coefficient pointer */
    q7_t *px, *pb;                                 /* Temporary pointers to state and coeff */
    q31_t acc = 0;                                 /* Accumlator */
    q7_t *pStateCurnt;                             /* Points to the current sample of the state */


    /* S->pState points to state array which contains previous frame (numTaps - 1) samples */
    /* pStateCurnt points to the location where the new input data should be written */
    pStateCurnt = S->pState + (numTaps - 1u);

    /* Initialize blkCnt with blockSize */
    blkCnt = blockSize;

    /* Perform filtering upto BlockSize - BlockSize%4  */
    while(blkCnt > 0u)
    {
        /* Copy one sample at a time into state buffer */
        *pStateCurnt++ = *pSrc++;

        /* Set accumulator to zero */
        acc = 0;

        /* Initialize state pointer of type q7 */
        px = pState;

        /* Initialize coeff pointer of type q7 */
        pb = pCoeffs;


        i = numTaps;

        while(i > 0u)
        {
            /* acc =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */
            acc += (q15_t) * px++ * *pb++;
            i--;
        }

        /* Store the 1.7 format filter output in destination buffer */
        *pDst++ = (q7_t) __SSAT((acc >> 7), 8);

        /* Advance the state pointer by 1 to process the next sample */
        pState = pState + 1;

        /* Decrement the loop counter */
        blkCnt--;
    }

    /* Processing is complete.
     ** Now copy the last numTaps - 1 samples to the satrt of the state buffer.
     ** This prepares the state buffer for the next function call. */


    /* Points to the start of the state buffer */
    pStateCurnt = S->pState;


    /* Copy numTaps number of values */
    i = (numTaps - 1u);

    /* Copy q7_t data */
    while(i > 0u)
    {
        *pStateCurnt++ = *pState++;
        i--;
    }

#endif /*   #ifndef ARM_MATH_CM0_FAMILY */

}

/**
 * @} end of FIR group
 */
